1. Field of the Invention
The present invention relates generally to electromagnetic relays, more particularly, to a miniature power switching relay specifically designed for mounting on printed circuit boards. The present invention utilizes a pressure spring inserted into the relay housing for pressuring a center contact spring into position and providing for normally contact pressure without pre bending the center contact spring. The present invention further utilizes ultrasonic welding of the copper terminals and the center contact springs as well as the copper terminals and the normally open and normally closed contact springs creating higher conductivity properties and greater contact area.
2. Description of the Prior Art
Electromagnetic switching devices, commonly referred to as relays, have been used for many years and there is a continuing need for such a device which is small in size. Yet, moreover, there is a need for such a device capable of reliably handling relatively high current switching jobs. This requirement for miniaturization together with higher contact rating reliability has become particularly important in recent years because of the increasingly common practice of mounting relays on printed circuit boards.
In the design of an electromagnetic relay and other such electromagnetic devices an important consideration is the design of the "magnetic circuit." The design of an effective magnetic circuit determines to a great extent the current switching capability of the relay and the power needed to operate it. The magnetic circuit of a relay generally includes the core inside the relay coil, the relay frame and the armature that moves an actuator, and then the actuator moves the relay contacts. In addition, air gaps exist between the armature and the core of the relay coil at an exposed end.
In relay operation electrical current is sent throughout the relay coil. The current running throughout the relay coil sets up a magnetic field in this magnetic circuit and it is the strength of the magnetic field generated in the air gap between the armature and the core inside the relay coil at an exposed end that is the force that causes the armature to move into contact with the core inside the relay coil at an exposed end providing the motion to operate the switching of the relay contacts. In the relay, the core inside the relay coil, the frame and armature are made of materials that can be easily magnetized and has low residual magnetism. The air gaps, however, resist the establishment of a magnetic field, and the air gap between the armature and the core inside the relay coil has by far the most significant resistance to a magnetic field in the magnetic circuit. In obtaining switching capability for the relay, it is desirable to design effective contact travel distances and rapid movement of the contacts by the armature. It is also desirable to provide the strongest possible magnetic field at this armature gap for the available coil current. This provides for positive and rapid contact movement. A strong return (pressure) spring allows for return movement of the armature when the relay current is removed causing positive and rapid contact movement.
Therefore, the mechanical arrangement of the magnetic core, relay armature, resulting air gap and the design of their interfaces significantly affect the ability of the relay to perform its function as an electrical switching device. It is desirable to maintain a minimum air gap between the core and the armature. This air gap must be tailored to the design of the relays function achieving the intended movement needed to move the center contact spring(s) with the center contact rivets to the required distance for proper contact switching.
Conventional relays presently on the market use a center contact spring with single headed contact buttons for normally closed and normally open contact arrangement or with double headed contact buttons for change over contact arrangement. The center contact spring is pre bent to achieve the necessary contact pressure and to hold the actuator in place of the relay where the pre bent center contact spring holds down above the actuator to contact the rivet of the normally closed contact spring. The overtravel is the distance between where a rivet of the center contact spring starts to contact a rivet of either the normally closed spring or normally open spring and where the contacting rivets reach stable position. This overtravel causes contact wiping between the contact areas of a rivet of the center contact spring and corresponding contact areas of rivets of either the normally closed spring or normally open spring.
Overtravel and contact wiping are essential in a relay for better reliability and longer life of the relay. The overtravel is necessary to make sure that burned off or evaporated material, which occurs at every switching operation, is eliminated. The overtravel further causes contact wiping which cleans the contact surfaces. At every switching operation, a micro weld is formed which needs to be broken when the contact is supposed to open. To break these micro welds, a shearing force is provided by the contact wiping. To achieve the overtravel, a minimum contact force is required. This required contact force is generated by the deflection of the pre bending of the center contact spring in conventional relays.
Pre bending of the center contact spring, though, contains limitations. The pre bending results in limits of the flexibility and deflection of the center contact spring. In order to achieve the required contact pressure for the overtravel and to hold the actuator down in the un-energized state, a minimum deflection is required. Based on the material characteristics of the center contact spring, a maximum deflection of the center contact spring is allowed before the center contact spring loses its spring property partially, which means that the center contact spring will no longer be able to return to its original position. Thus, the center contact spring may be stressed beyond its limits resulting in loss of contact pressure and causing the failure of the relay. In order to remedy this situation, conventional relays reduce the thickness of the center contact spring which results in reduced contact pressure, reduced overtravel, reduced center contact spring cross section and reduced contact rating.
The present invention fulfills the need for a device, which is small in size, yet capable of reliably handling high current switching jobs relative to known designs. The present invention solves the high current problem in a small size by using a combination contact assembly with a pressure spring.
Further, in conventional relays, it is known that bi-metal contact assemblies are used in electromagnetic relays. These known electromagnetic relays use bronze and brass materials for the springs and terminals. In addition, the springs and terminals are spot welded together.
A problem with the known brass and bronze materials is that these materials have low current conductivity properties. In addition, spot welding produces a limited contact area for the electrical current to flow through between the springs and the terminals resulting in lower current handling potential. During assembly, it is difficult to join the springs as single entities with almost no electrical resistance between the connections. Low electrical resistance is required if high electrical current is carried over these contact spring assemblies. The difficulty in assemblies lies in the high electrical conductivity of the individual springs and terminals, which do not allow for spot welding. Even if spot welding were possible, the springs are only connected during spot welding by small areas, which would then become bottle necks for the current flow.
U.S. Pat. No. 5,160,910 issued to Tsuji discloses an electromagnetic relay comprising a relay motor, an armature interacting with the relay motor, an actuator, first and second terminals, contact springs, and a center contact spring assembly. In this relay, the relay motor moves the armature by electromagnetic force, which in turn moves the actuator. The actuator moves the center contact spring to contact either the first or second terminal to complete the current flow.
This relay contains limitations, though. First, the contact springs are not made from a high conductive copper alloy and the terminals are not made from pure copper. Further, the contact springs and terminals are spot welded together as opposed to ultrasonically metal-to-metal welded to each other. Thus, the relay is comprised of less conductive material with less contact surface between the springs and terminals as they are not ultrasonically metal-to-metal welded together.
Further, the relay utilizes a pre bent center contact spring as opposed to a pressure spring to hold the center contact spring in place while the actuator is not acting on the pre bent center contact spring. Thus, the relay has less overtravel resulting in a shorter relay life. The pre bent contact spring does not allow for 1.5 mm resp. 3.0 mm contact gap, which is required by VDE, TUV and other certifying agencies when the relay is used for certain applications.
U.S. Pat. No. 5,250,914 issued to Schedele discloses an electromagnetic relay comprising a contact system, an armature and actuator. In this relay, the contact system which contains at least one movable contact element is mounted inside the housing by a clamp or glue joint or by ultrasonic welding. Further, the armature and actuator can be connected by an ultrasonic weld.
This relay also contains limitations. First, the contact springs are not made from a high conductive copper alloy and the terminals are not made from pure copper. Further, the relay utilizes a pre bent contact spring as opposed to a pressure spring to hold the center contact spring in place, and provide the necessary normally closed contact pressure. The pre bent contact spring in prior art does not allow for 1.5 mm resp. 3.0 mm contact gap, which is required by VDE, TUV and other certifying agencies when the relay is used for certain applications. Also, the relay has less overtravel resulting in a shorter relay life. Further, the ultrasonic welding disclosed in the prior art does not ultrasonically weld the contact and springs to provide greater contact surface for conductivity. Still further, the ultrasonic welding disclosed in the prior art does not even provide a metal-to-metal ultrasonic welding. The ultrasonic welding disclosed only refers to attaching the spring assemblies to the housing and to attaching the actuator to the armature, which has to be made from plastic or non-electrically conductive material.
Accordingly, there is a need for an electromagnetic relay that is small in size yet capable of handling high current switching and also with 1.5 mm resp. 3.0 mm contact gap.
Accordingly, there is also a need for an electromagnetic relay with a contact assembly comprised of more conductive material than brass and bronze and having a greater contact surface between the springs and the terminals.
Accordingly, there is also a need for an electromagnetic relay without a pre bent center contact spring.
Accordingly, there is also a need for an electromagnetic relay with large contact gap.
Accordingly, there is also a need for an electromagnetic relay with higher switching and operating current.
The present invention solves all of these problems. First, the springs and terminals are made of high current conductive materials namely copper alloys with maximum spring properties and pure copper. Secondly, the parts are ultrasonically metal-to-metal welded together which produces a large contact area between the springs and the terminals resulting in higher current handling potential. Thirdly, a pressure spring is inserted into the housing for producing the required normally closed contact pressure without pre bending the center contact spring. Therefore, by using materials with high conductivity properties and increasing the contact area between the terminal and the spring and using a pressure spring, the present invention can handle higher currents while maintaining a relatively small overall package size. The present invention can handle at least 25 amps in a single pole embodiment and at least 12.5 amps in a double pole embodiment.
The pressure springs allow for less deflection of the center contact springs, therefore, thicker contact springs resulting in higher switching and operating current. The pressure springs also make it possible to significantly increase the contact gap. For example, contact gap of 1.5 mm resp. 3.0 mm can be provided in the relays by using present invention. These contact gaps are required by VDE, TUV and other certifying agencies when the relay is used for certain applications. The large contact gap is also desirable for high voltage DC switching. In order to increase the switching and operating current while minimizing the heat generated by higher currents only two options are currently available. One is to make the center contact spring wider, which requires an increase in the overall size of the relay. The other is to increase the thickness of the center contact spring, which results in higher bending force requiring a stronger relay motor which also requires an increase in the size of the relay.
Some other conventional relays employ a latching magnetic motor. There are a few designs for latching magnetic relays currently in the prior art. These latching magnetic relays typically include a relay motor assembly that is magnetically coupled to the actuator. The relay motor typically drives the actuator, which in turn drives the center contact rivet of the center contact spring into the rivet of the normally open spring.
Also, current latching magnetic relay typically have relay motors, which generate a rotational movement. Center contact springs typically require only a linear movement in the actuator assembly to bring it into contact with the opposite contact areas. Consequently additional parts are required in order to convert the rotational movement generated by the relay motor into a linear movement, adding to the expense of producing and assembling the latching magnetic relay.
Accordingly, there is also a need for a small latching magnetic relay with a motor that generates a linear movement to accommodate contact assemblies, which require only a linear movement while utilizing a pressure spring for the center contact spring.
Accordingly, there is also a need for a latching magnetic relay with a contact assembly comprised of more conductive material than brass and bronze and having a greater contact surface between the springs and terminals.
As will be described in greater detail hereinafter, the present invention solves the aforementioned and employs a number of novel features that render it highly advantageous over the prior art.